Lab 28: IPv6 SLAAC — Auto-Addressing Without DHCP
IPv6 hosts can configure themselves: with SLAAC (Stateless Address Autoconfiguration), the router advertises the prefix and hosts self-generate a full address — no DHCP server needed. Difficulty: Intermediate · Time: ~25 min.
Lab objectives
- Enable IPv6 routing and address the router interface
- Understand router advertisements (RAs)
- Set PCs to IPv6 autoconfig and watch addresses appear
- Verify gateway learning without any DHCP
Topology & addressing
1× router (Gi0/0 = 2001:db8:cafe:1::1/64), 1× switch, 2× PCs set to IPv6 Automatic.
Step-by-step configuration
ipv6 unicast-routing | Enables routing AND router advertisements |
interface gi0/0ipv6 address 2001:db8:cafe:1::1/64no shutdown | The advertised prefix comes from this address |
| PCs → IPv6 Configuration → Automatic | Watch each PC self-generate 2001:db8:cafe:1:xxxx… |
Verification
Each PC shows a global address combining the router's /64 prefix with a self-generated interface ID — plus the router's link-local address as its gateway (learned from the RA, not configured!). PC-to-PC and PC-to-router pings work. No DHCP anywhere: that's SLAAC.
Next lab: labs hub · test yourself: CCNA practice test.
Frequently asked questions
How does a host build its SLAAC address?
It combines the /64 prefix from the router's advertisement with a self-generated interface identifier — historically EUI-64 from the MAC, now usually a random/privacy value.
Where does the host's default gateway come from in SLAAC?
From the router advertisement itself — hosts use the router's link-local address as gateway, with zero manual configuration.
When is DHCPv6 still needed?
When you need to assign options SLAAC doesn't provide (like DNS servers, on platforms without RDNSS support) or want centralized, logged address assignment.
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